Apparatus for broaching spiral gears



June 14, 1960 K. E. EKLUND APPARATUS FOR BROACHING SPIRAL GEARS 8Sheets-Sheet 1 Filed April 7, 1955 IN VEN TOR.

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APPARATUS FOR BROACHING SPIRAL GEARS Filed April 7. 1955 8 Sheets-Sheet8 United States Patent 1 2,940,159 APPARATUS FOR BROACHING SPIRAL GEARSKarl E. Eklund, 14333 Prairie, Detroit, Mich. Filed Apr. 7, 1955, Set.No-,499,780 16 Claims. (Cl. 2995.1)

This invention relates to a method and apparatus for breachingindividual spiral gears.

:In many applications for gears, especially in the automotive industry,it is important that the cost be reduced to a minimum for use especiallyin window raising assemblies and other similar applications. It isimportant to have a low-cost gear which will be serviceable. It is alsodesirable to have a spiral gear which, of course, provides a smootheroperation.

It is an object of the present invention to provide a method andapparatus for breaching spiral gears. I have previously developed thebreaching of straight-tooth gears, such as spur gears and the like, andbreaching dies having internal teeth are known in the art in suchpatents as 1,070,561 to W. R, Walker, August 19, 1913. Some of thesedies use special rings cut to shape and heat treated. With this type,warping and distortion frequently change the shape of the ring, causinginaccuracies. Also, chip removal is difiicult because of lack ofclearance.

It is an object of the present invention to provide an improvedbreaching die which can be manufactured and assembled at considerablyless expense than an ordinary breaching cutter which may be especiallymade for a particular job out of a solid piece.

It is a further object to provide a breaching die in which the teeth maybe simultaneously ground in a special type of holder, and a furtherobject to provide an assembly wherein the damaging of one tooth will notdestroy the entire cutter. Also, it is an object to provide a dieassembly in which chip removal is possible with out packing of the chipsin the tool.

Another object is the provision of a breaching die with internal teethwhich will cut a spiral gear without the necessity of independent leadcontrol, the spiral resulting from the inherent nature of the teeth andthe arrangement in the die or breaching holder. The result is anapparatus and method of breaching spiral gears which permits theirproduction from prepared blanks at the low est possible cost at whichany machineahle gears may be produced and yet with an accuracy which ismaintained equal to or better than gears made in a hobbing operation.Other objects and features of the invention relating to details ofconstruction and operation will be apparent in the following descriptionand claims.

Drawings accompany the disclosure, and the various views thereof may bebriefly described as:

Figure 1, an assembly view of the device showing the relationship of theparts.

Figure 2, a sectional view on line 22 of Figure 1.

Figure 3, a longitudinal section adjacent the feed end of the devicetaken on line 3-3 of Figure 2.

Figure 4, a sectional view of the die with the blank nearing completiontaken on line 44 of Figure 1.

Figure 5, an elevation of thedie head at the feed end taken on line 55of Figure 1.

Figures 6, 7 and 8, an end view and side elevations of an individualtube used in the die assembly.

Figure 9, a view of the breach body showing the helical position linesfor the cutter plugs.

Figure 10, an end view of a completed spiral gear.

Figure 11, a side view of a completed gear.

Figure 12, a top view of a fixture used in grinding the cutting teeth.

Figure 13, a side view of the grinding fixture showing the manner inwhich the teeth are graduated.

. to conform to the cutter body 2%. The body can be 2,940,159 PatentedJune 14, 1960 Figure 14, a diagrammatic view of an enlarged grooveshowing the progressive cuts taken in the breach assembly.

Figure 15, an elevation of one end of a breach assembly showing aring-type clamp.

Figure 16, a sectional view showing the manner in which the ring clampacts on the breach plugs.

Figures 17 and 18, bottom views of a grinding fixture showing the mannerin which the teeth are interspersed with aligning plugs for grinding.

Figures 19, 20 and 21, diagrammatic views showing the various dimensionson the grinding plugs.

Figures 22, 23 and 24, charts corresponding respectively to Figures 19,20 and 21 showing relative dimensions on the diagrammatic views.

Figure 25, a modified body construction illustrating an alternative wayof aligning the tooth plugs independent of each other.

Figure 26, a fragmentary section showing the body construction of Figure25.

Figure 27, a section on line 27- 27 of Figure 26.

Figure 28, a perspective view of a modified body con struction.

Figure 29, a view of a tooth plug to be used in the body of Figure 28.

Referring to the drawings, attention is drawn first to Figure 9, whichshows a breach cutter body as a cylinder 20 having a manifold groove 22for distributing coolant around the body to passages which lead to thecenter thereof. In Figure 9, lines 24, 26, 28, 30, and so. forth, showthe helical path for the various cutter plugs. which are to be insertedin the body.

In Figures 10 and 11, the spur gear 32 is shown which is to be cut, thisgear having nine teeth with a helical shape. The blank from which thespur gear is made is of cylindrical shape having the diameter of thespur gear. tral passage 40 of the breach body 20. The breach body 20, asshown in Figure 2, is bored radially around its circumference with aplurality of holes 42, each successively spaced along the helical linesof Figure 9. There are nine rows of holes spaced around the body, eachon a helical line which runs the length of the body. each of the rolesthere is inserted a cylindrical toothed cutter plug 44 having a head 46at one end and a tooth formation 50 at the other end. The particularformation of the cutter teeth will be described later, it beingsuificient to say at this time that they vary in length andconfiguration from one end of the breach body to the other.

Beneath the head of each tooth cutter is a spacer 52 having a fiat topsurface and a curved bottom surface ground with a fiat outer surface, inwhich case, fiat shims could be used. These spacers or shims 52 simplifythemanufacture of the plug heads and also permit a re-grind on the teethby substituting spacers of a lesser thickness. This permits a re-use ofthe expensive teeth after a wear period. One manner of holding the teethin place is shown in Figure 2, in which an anchor yoke 54, held in placeby a bolt 56, has projecting points 58 which reach to the center of eachplug to hold it securely in place.

The plugs are held in place in pairs throughout the length.

, flats on the cutter teeth will contact each other in assem- This blankis to be pushed through a can tion.

bly, each tooth thus locating and stabilizing the next adjacent toothand so on throughout the entire construc- The broach body is suitablymounted in a head 60 (see-Figure 1.) through which cooling fluid may befurnished to the manifold groove 22. Associated with the head is aplunger 62 having a plunger rod 64 rotatably mounted thereon so that itmay turn as it pushes the blank through the breach. A coolant fluidpassage 65in head 60 furnishes coolant to the manifold groove 22,whererit passes to tangent holes 66 which tend to move coolant in thedirection of the spiral and insure chip flow to the discharge 'end.

The head 60 (Figure 5,) has a feedchannel 67 to receive gear blanks froma hopper feed (not shown). A pltmger 68 is periodically actuated to movea blank up to position where the rod 64 can start it on its path throughthe breach.

In order to broach spiral teeth on a gear, it is necessary that the gearbe properly guidediand turned. It will be recognized that the lead angleof a spiral gear tooth changes from its root to its outer diameter. .Itis necessary, therefore, to get this varying angle from the innerdiameter to the outer diameter. In the present case, this isaccomplished by grinding the teeth with varying cutting depths andangles and providing an unusual tooth design which imparts the necessaryspiral motion to the gear as it moves through the broach. The grindingcan also be done in this fixture to provide the necessary back-oilangles and contour. For example, in Figures 6, 7 and 8, a typical toothis shown. The tooth is ground away to provide a gullet at 70 to providechip space and is ground on the side at 72 and 74 to provide sideclearance. The tooth may be hollow ground on top at 76, and the sidesare'ground at an angle so that the leading edge 78 has a leading corner8%) and a trailing corner 82. The edge 78 is at a shear angle whichtends to move the blank in proper rotative action for spiral cutting.The direction of the work relative to the tooth is shown on the dottedline AB in Figure 6, and from this it will be seen that there is aback-oil clearance on the edge 84 behind the lead corner 80.

The edge 86 behind the trailingcorner 82 is not backedoff but actuallyforms a slight heel which also moves the leadcorner 80 into the work mdcreates the spiral motion of the work as it progresses. In Figure 2 theshape of the teeth used for the introductory cuts on the blank is shown.In Figure 4 the shape of the teeth for the final cuts is shown.

The blank is pushed through the lead portion of the body 20 by therod64, and the blank turns in response A to the cutting action of theteeth, being'uncontrolled in its turning except by the teeth which areacting on it.

In- Figure 14 the progress of the cuts is shown by dotted lines. Thefirst teeth in the series will make curved cuts, as indicated in thearea from 1 to 15m Figure 14. These curved teeth take a side cutimmediately on the cylindrical surface and thus cause movement of theblank'in the spiral direction. The teeth from 15 to 24 are straight intheir outer contour, since it is less expensive 'to form a tooth in thisway and the guidance can come out the sides as these teeth progress intothe tooth form. The cuts from 24 to 32 gradually narrow following thetooth form. The cutsfrom 32 to 44 also follow the tooth form approachingthe root diameter and also start'cu-ttingthe final outer contour of thetooth adjacent the OD. The-final four teeth are guided on the sides ofthe iteeth adjacent the pitch line and are also curved to further insureaccurate spiral progress and clean out the root of the teeth to finishthe job. Teeth from about 43 to 52 start shaving the sides of the toothto the final form along'the'heavy black line. .It is desirable'that thefinal teeth have a slight back-off oneachside to insure a finish cut onboth sides of the'gear teeth. 7 V

The lead angle of the teeth must vary as the cut gets deepersince in a;spiral cut the lead may be close 'to.

8de'gre es at the O. D., 6% deg're'es at thepitch' line, and

5 degrees at the root of the tooth. In fact, as the out begins-it isdesirable to have the blades at greater angle than true lead tocompensate for lag or slippage in the rotation of the part. The lead atthe cutting edges, except at the start, is about equalto that ofthe geartooth at the cut audit: is possible to back off the remainder of thecutting tooth so it will not interfere at; the higher angles at theouter ends of the gear teeth. With the disclosed method ofg'riii'dingocfteeth, it will be seen, a backoil can be readily provided at any point.

It is desirable when poss'ble to have-two teeth in the gear groovesatany one time, and this assists in thelead turn of the blankalthough'it is possible to control this lead turn without such acondition. a H

In Figures 12 and 13 and 17 to 24, there" is shown a method of arrangingthe teeth for proper grinding in a fixture. The tooth plugs are arrangedin side by-side position aligned in a fixture. They are disposedatanangle by the ends of the fixture and at angles. to. each other by dummyplugs interposed as shown. With this arrangement a straight pass of thegrinding wheel will put the proper side angle on the teeth. As showninFigure 12, it is desirablethat the centerline of the plugs coincide Vwiththe centers of the cutting corners of the teeth; Then;

when the teeth are arranged in the spiralled holder, the cutting. edgeswill fall in a proper spiral.

The lay-out of Figures 17 to 24 shows a set-up for a 6 /2 degree helix,nine tooth RH. gear form. The various teeth from T1 to T52 are setat'varying angles by end plates 100 and dummy plugs R-1, R2', and soforth. The charts and plug ends'show the varying angles used in thegrinding operation.

With the teeth ground as above described, the gear 1 blank can be pushedthrough the'broach and it will turn at the proper rate to'produce anaccurate helix gear; With respect to'the method of operation, it shouldbe further stated that concentricity can be perfectly malntairled,ifdesired, by inserting circumferentially spaced dummy guideplugs,z-three, for example, for the first pass, so that six teeth couldbe cut. The last three teeth could then be cut using guide plugs in thecutrecsses to maintain concentricity.

In Figures 15 and 16, a modified construction is shown wherein the teeth44 are held in body"20 b'y'a-plurality ofsolid rings 110, whichare'driven'on the assembly over In Figures 25'to' 27, there is showmanalternative body construction in which heads 46" of the broach teeth arereceived iii'surface' slots -on thefbody 122 at the outer endsofholes"124:= These slots 129' are spaced axially to leave Icircumferential ridges1 26 which lock theflat sides of the heads'46in adefined position. This permits independentpo'sitioning of'e'acl'rtooth.V

In Figures 28 and 29, amodified'body construction is shown wherein thebody is provided with spiral surface slots 134. which receive flat sides132 urine hadnd of the tooth plugs 134 to locatethe same; Hereagainueteeth may be pos'ition'ed independentlyand clamped as previouslydescribed.

When the term spi ral gear is' used herein, it maybe taken to mean "anybody having spaced spiral' slots and spiral flutes regardless of'theparticular tooth formation. The method and apparatus herein actuallyform's spiral sl'o'tsin a leavingspiral gear teethor splines or'othrshapes'o'f 'tootli-likfiiit's; t

I claim:

1. An apparatus for forming and finishing external gears by broachingoperation, which comprises a cylindrical broach body of one pieceintegral elongate construction having a central axial opening, aplurality of radial round recesses in said body spaced circumferentiallyand axially along and intersecting said opening, a plurality ofbroaching teeth each externally insertable and removably positionedindependently of the other in a recess in said broach body and eachcomprising a cylindrical body shank portion snugly fitted in one of saidradial recesses having one end projecting into said opening as a toothform, another portion of each of said teeth being acircular in shape toserve as a locator to prevent rotation of the teeth within the recesses,means positively to position said teeth in a defined position radiallyof said holder, and releasable means to hold said teeth in said radialposition.

2. An apparatus for forming and finishing external gears by a broachingoperation, which comprises a broach body of elongate construction havinga central axial opening, a plurality of radial recesses in said bodyspaced circumferentially and axially along and intersecting saidopening, a plurality of broaching teeth each removably positionedindependently of the other in a recess in said broach body and eachcomprising a body shank portion snugly fitted in one of said radialrecesses having one end projecting into said opening as a tooth form,another portion of each of said teeth being acircular in shape to serveas a locator to prevent rotation of the teeth within the recesses, meanspositively to position said teeth in a defined position radially of saidholder, and releasable means to hold said teeth in said radial position.

3. A device as defined in claim 2 in which the means to positivelyposition the said teeth comprises on each tooth a head at the outer endto limit the inward radial movement of the tooth form in the axialopening.

4. A device as defined in claim 2 in which the releasable means to holdsaid teeth in said radial position comprises clamping blocks bearing onthe outer ends of said teeth and means anchored in said broach bodyexerting inwardly radial force on said blocks and said teeth.

5. A device as defined in claim 2 in which the said I acircular portionof each of the plurality of teeth comprises radial mating surfaces onthe outer ends of said teeth positioned outside said recesses tointerengage adjacent teeth.

6. A device as defined in claim 2 in which the said acircular portion ofeach of the plurality of teeth comprises a head larger than saidrecesses to position outside said recesses, having planer matingsurfaces perpendicular to the axis of said body positioned axially tointerengage similar surfaces of adjacent teeth.

7. A device as defined in claim 2 for cutting of spiral tooth gears inwhich the radial recesses in the body are arranged along a plurality ofspiral lines axially of said body, said lines being spacedcircumferentially to correspond with the number of teeth to be formed.

8. A device as defined in claim 7 in which the tooth form on each toothprojecting into the axial opening and thus into the path of portions ofthe gear blank comprises a straight sided, quadrilaterally outlinedplateau area gradually ensmalled from the body shank, having a forwardshear edge at an angle to the path of the blank, the lead corner of saidshear edge being followed by a side edge relieved to permit cutting, thetrailing corner of said shear edge being followed by a side edge forminga heel to move the lead corner into the work to impart a relativerotation between a gear blank and the body as the blank passes the toothforms.

9. A device as defined in claim 7 in which the tooth form on the broachteeth is shaped with a quadrilateral form having a lead corner and atrailing corner at a forward cutting edge which is angled from the leadcorner to the trailing corner, the side edge of the form adjacent thelead corner being relieved and the side edge of the form adjacent thetrailing corner being disposed in approximate parallel relation to theother side edge wherein the tooth imparts a relative rotative motionbetween the body and a gear blank moving through the body.

10. A device as defined in claim 8 in which the surface between theshear edge and the shank of the tooth is undercut to provide a slighthook at the shear edge.

11. An apparatus as defined in claim 8 in which the tooth forms areshaped progressively from one end to the other of the body to graduallyremove the metal between the teeth of the finished gear, theinitialteeth being dimensioned to remove material spaced from the sidesof the finished teeth and progressively to move radially inward andcircumferentially outward to the final tooth form.

12. An apparatus as defined in claim 11 in which a plurality of teeth atthe entrance to said opening have the face surface of the cutting edgescurved concavely to create side edges projecting radially beyond thecenter of the tooth form.

13. An apparatus as defined in claim 11 in which a first group of teethat the entrance to said opening are located at a spiral lead anglegreater than the desired lead of the tooth, and a plurality of teethbeyond said first group are positioned at a lead angle substantiallyequal to the desired lead of the tooth at the point of cut.

14. An apparatus as defined in claim 11 in which the forward cuttingedges of the tooth form are shaped to conform approximately to thespiral angles of the teeth being cut radially at the point of cutting,the other form below the cutting edge being backed off to permitclearance of that portion of the formed tooth outside the point ofcutting which has a greater spiral angle.

15. A broach tooth to be held in a breaching body for use in cuttingspiral slots on a blank to be used as a spiral gear, which comprises anelongate body to be held radially in a broach holder, said body having alocating shank portion, a tooth formation at one end comprising astraight sided, quadrilaterally outlined plateau area graduallyensmalled from the body shank, the sides of said plateau lying in aplane substantially perpendicular to the axis of the tooth body, saidtooth having a forward shew edge connecting said side edges, forming alead corner and a trailing corner, the side edge adjacent said leadcorner being angled to a relief position, the side edge adjacent saidtrailing corner being angled to a heel position in approximatelyparallel relation to the first side edge.

16. A broach tooth as defined in claim 15 in which the end of the toothopposite the tooth form is shaped with fiat surfaces lying in a planeoutwardly from the shank portions and parallel to the axis of the shankto engage with similar surfaces on adjacently positioned spaced teeth.

References lite-d in the file of this patent UNITED STATES PATENTS772,841 Smith Oct. 18, 1904 1,089,376 Hanson Mar. 3, 1914 1,986,793Chapman et a1. Jan. 8, 1935 2,102,071 Hart Dec. 14, 1937 2,161,901 PraegJune 13, 1939 2,282,193 Lambrix May 5, 1942 2,304,185 Lee Dec. 8, 19422,346,851 Lloyd Apr. 18, 1944 2,374,890 Pelphrey May 1, 1945 2,511,298Schinnerer June 13, 1950 2,536,864 Strickland et a1. Jan. 2, 19512,641,822 Sampson June 16, 1953 2,644,369 Praeg July 7, 1953 2,674,780Nielsen Apr. 13, 1954 2,683,919 Psenka July 20, 1954

